Magenta inks

ABSTRACT

The present disclosure is drawn to a magenta pigment blend, a magenta ink, and a method of formulation a magenta pigment blend. The magenta pigment blend can be a first pigment including a solid solution of Pigment Violet 19 and Pigment Red 122, or Pigment Red 282; and a second pigment including Pigment Red 150. The weight ratio of the first pigment to the second pigment can be from 50:50 to 80:20 by pigment solids content.

BACKGROUND

There are several reasons that inkjet printing has become a popular wayof recording images on various media surfaces, particularly paper. Someof these reasons include low printer noise, capability of high-speedrecording, and multi-color recording. Additionally, these advantages canbe obtained at a relatively low price to consumers. Though there hasbeen great improvement in inkjet printing, accompanying this improvementare increased demands by consumers, e.g., higher speeds, higherresolution, full color image formation, increased stability, largeformat printing, etc.

A few characteristics of inkjet printing systems that are desirable toachieve relate to nozzle health, short term and sustained decapperformance, kogation, color gamut, durability, ink efficiency, to namea few. Accordingly, investigations continue into developing inkformulations that can be printed accurately and with acceptabledurability without excessive clogging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example a*b*CIE Color Coordinate Plot in accordance withexamples of the present disclosure;

FIG. 2 is an example graph that illustrates saturation value curves formultiple colors for various weight ratios of quinacridone and azopigments in accordance with examples of the present disclosure; and

FIG. 3 is an example graph that compares commercially available inkswith inks sets that include magenta pigment blend-based magenta inks inaccordance with examples of the present disclosure.

DETAILED DESCRIPTION

The present disclosure is drawn to magenta inkjet inks which include ablend of multiple magenta pigments. In preparing magenta inks generally,the selection of a pigment can be such that it exhibits acceptable colorproperties. However, formulating an inkjet ink with appropriatesolvents, surfactants, and other liquid vehicle components with anappropriate pigment that performs well in every color space is not assimple as selecting components and admixing them together. For example,a magenta pigment can be selected to produce an acceptable red colorwhen combined with a yellow pigment in a typical ink jet printer systemmay not necessarily have good color strength in the blue or violetregions when mixed with cyan pigments. On the other hand, a differentmagenta pigment that may have good color strength in the blue and violetregion when combined with a cyan pigment may be deficient in the redregions (again, when combined with yellow). In either case, the overallcolor gamut is when the selected pigment or pigment dispersion does notperform well along the entire color spectrum, causing an observer of aninkjet print to be dissatisfied due to either too little or red or toolittle blue color. By blending various magenta pigments together, atradeoff between acceptable blue and acceptable red color strength canbe achieved.

With this background in mind, in accordance with the examples describedherein, various details are provided herein which are applicable to amagenta ink, a magenta pigment blend, and a method of formulating amagenta ink of the present disclosure. In one example, a magenta ink caninclude a liquid vehicle including water, organic co-solvent, andsurfactant, and the magenta ink can from 2 wt % to 9 wt % of magentapigment blend suspended in the liquid vehicle. The magenta pigment blendcan include quinacridone pigment and azo pigment. The quinacridonepigment can have the general structure:

wherein R₁ and R₂ are each independently H, a halogen atom, or a C₁ toC₄ alkyl group. The azo pigment can have the general structure:

wherein R_(a) is H, aryl, or C₁ to C₄ alkyl, but when R_(a) is aryl, thearyl is not a phenyl group having at least one hydrogen that has beensubstituted with a chlorine atom; and wherein R_(b), R_(c) and R_(d) areindependently H, a C₁ to C₄ alkyl, an oxygen-containing functionalgroup, a nitrogen-containing functional group, or a sulphur-containingfunctional group. With these magenta inks, to balance the red and bluecolor strength of the magenta color, the weight ratio of quinacridonepigment to azo pigment can be from 50:50 to 80:20 by pigment solidscontent. It is noted that there can be multiple quinacridone pigmentand/or azo pigments in the magenta ink (or magenta pigment blenddescribed hereinafter), and it is the total weight percentage ofquinacridone pigment and/or azo pigment that is used to calculate theweight ratio of pigments as well as pigment solids concentration in theink as a whole.

In another example, a magenta pigment blend can include a solid solutionof quinacridone pigment, namely Pigment Violet 19 and Pigment Red 122,or Pigment Red 282; admixed with azo pigment, namely Pigment Red 150.The weight ratio of the quinacridone pigment to the azo pigment can befrom 50:50 to 80:20 by pigment solids content. These pigments have thefollowing structures:

In another example, a method of formulating a magenta pigment blend caninclude co-dispersing a first pigment a second pigment together. Thefirst pigment typically has a stronger color strength in the red areasof CIE Color Coordinate Plot compared to its color strength in the blueareas, and the second pigment typically has stronger color strength inblue areas compared to its color strength in red areas. The firstpigment and the second pigment can be co-dispersed at a weight ratio toimprove color strength in the blue areas compared to the first pigmentand to improve color strength in the red areas compared to the secondpigment. By “stronger” color strength, what is meant is a larger colorsaturation, defined as the chromaticity divided by the lightness (CIEC*/L*)VO at a desired or predetermined hue angle. Typically for red, thehue angle can be from 30° to 15°, with the variability being dependenton the print media and end use. For blue, the hue angle can be from 260°to 280°, again depending on the media and application. In one example,the hue angle for red can be measured at 17° and for blue at 270°. As anexample, for red, a saturation of greater than 0.71 can be desirable andfor blue a saturation of greater than 0.64 can be desirable. FIG. 1illustrates the problems associated with red color strength and violetcolor strength. Specifically, two pigment dispersion types wereevaluated (quinacridone and azo separately), and then a blend of the twopigment dispersions (quinacridone and azo together) were also evaluated.As can be seen in the FIG. 1, within the yellow and green regions bothquinacridone pigment and azo pigment perform very similarly (when mixedwith other inks appropriate for generating those colors), and it is onlyin the blue to violet to red regions where the two types of pigmentdispersions separate in their color profile. By blending the pigments atabout a 70:30 weight ratio (quinacridone pigment to azo pigment), anacceptable average red, violet, and blue can be achieved that isrelatively close in color to each of the pigment dispersions alone. Theratio can alternatively range from about 50:50 to about 80:20, byweight, with acceptable results as well. As mentioned, in this example,the quinacridone pigment is good for achieving good blue color strength,and the azo pigment works well for achieving good red color strength.Purple color strength ends up being more of an average between thatwhich is provided by both of the pigments, which is also made to be moreacceptable by the blending of these two pigment dispersions. Furtherdetails regarding FIG. 1 and can be found in the Examples.

As mentioned, although the problem of red and blue color strength can besolved to some degree by blending these two pigment dispersion together,the problem is not as simple as mixing the two materials. In order tohave good reliability and long storage life, the total amount (wt %) ofthe pigment solids in the ink should not be raised above normallyacceptable levels of total pigment solids. Thus, available mixtures ofquinacridone pigment and azo pigment can be formulated to follow theequation: wt % quinacridone pigment+wt % azo pigment=X. In thisequation, the wt % of azo solids can be at a concentration where the inkproduces an acceptable red color but more blue is needed, and wt % ofquinacridone solids can be at a concentration where the ink produces anacceptable blue color but more red is needed. Thus, as azo pigmentdecreases, the red color decreases but the blue increases asquinacridone pigment increases. At some point within the range ofblends, a ratio of azo pigment and quinacridone strikes a balance thatis pleasing to an observer in the blue regions and the red regions.

FIG. 2 illustrates various the weight ratios of quinacridone pigment toan azo pigment. As can be seen in this FIG., region A indicates an areawhere an acceptable color balance is struck between blues and reds,which corresponds to a weight ratio of 50:50 to 80:20 of quinacridonepigment to azo pigment. Also shown at region B, an alternative ratiorange is shown that also strikes a balance between the pigmentdispersions, which corresponds to a weight ratio range of about 65:35 to75:25. Further details regarding FIG. 2 and can be found in theExamples.

In accordance with another example of the present disclosure, thepigments described herein are selected or formulated so that they do nothave differential settling properties within the ink. If differentsettling profiles were present within the ink, then the pigment ratiowould change with time at various levels within the ink, resulting inunacceptable color shifts. Thus, in accordance with examples herein, thepigments can have similar dispersant technology associated with thesurface thereof, providing similar settling profiles. For example, allof the pigments present in the blend can be formulated to settle overtime. To validate this, the UV-vis mixture of the quinacridone pigmentand the azo pigment can have an absorbance maxima with a ratio dependenton the relative concentration of each. This ratio should remain constantwithin ±3% to be considered to have similar settling properties.

One advantage of utilizing the pigment blends of the present disclosureis that the inks prepared can be devoid of any dye, in one example.Without dyes, the durability and water or humid fastness can beimproved. Additionally, with these type of pigmented inks, no externalprinter assistance, such as special paper or extra fixer inks is needed,though they can be optionally used. This can simplify the printer systemand lower the cost of the entire system. Furthermore, printer systemcomplexity can also be decreased resulting in more reliable printers.Furthermore, since the weight ratio of the pigments can be modified,these inks can be adaptable to match the needs of future inkformulations and/or printers.

The pigments that can be used in accordance with embodiments of thepresent disclosure include both self-dispersed pigments as well asconventionally dispersed pigments, e.g., pigments dispersed by aseparate dispersing agent that is not covalently attached to thesurface. If self-dispersed, a dispersant is typically prepared in aprecursor form, and then the precursor is attached to the pigment tochemically modify the surface of the pigment. In one example, thedispersant can be attached to the pigment using various precursormaterials, such as para-aminobenzoic acids, isophthalic acids,tricarboxylic acids, carboxylic groups, sulfonylic groups, phosphates,oligomers, polymers, and isomers thereof, for example. Other precursorscan also be used to attach to the pigment, as would be known by thoseskilled in the art.

Typically, the pigments of the present disclosure can be from about 5 nmto about 10 μm in size, and in one aspect, the pigments can be from 10nm to about 500 nm in size, although sizes outside this range can beused if the pigment can remain dispersed and provide adequate printingproperties.

In further detail regarding the pigments, with inks generally, colorantsused to improve color gamut on the hue-saturation plane are often dyesrather than pigments. However, dye based inks can have poor durability(e.g. water fastness, light fastness, and air/ozone fastness). Inkjetink formulations prepared in accordance with the present disclosure,even without the presence of dyes, can have acceptable color gamut,while at the same time providing acceptable decap performance andimproved durability compared to dye-based inks.

Though the inkjet ink in each of these embodiments can be fired from avariety of different types of inkjet architecture, it is noteworthy topoint out that these inks can be fired very rapidly with improved decapperformance, and thus are suitable for printing from both carriage typeprintheads as well as printhead bars, such as page wide printheadassemblies or other print bars.

In further detail with respect to the surfactant, there are severalsurfactants that can be selected for use in the inkjet inks of thepresent disclosure. Non-limiting examples of suitable surfactantsinclude nonionic surfactant, cationic surfactant, and combinationsthereof. In one example, the surfactant can be a nonionic surfactant.Several commercially available nonionic surfactants that can be used inthe formulation of the pre-treatment composition include ethoxylatedalcohols such as those from the Tergitol® series (e.g., Tergitol® 15S30,or Tergitol® 15S9), manufactured by Dow Chemical; surfactants from theSurfynol® series (e.g. Surfynol® 104, Surfynol® 440 and Surfynol® 465),and Dynol™ series (e.g. Dynol™ 607 and Dynol™ 604) manufactured by AirProducts and Chemicals, Inc.; fluorinated surfactants, such as thosefrom the Zonyl® family (e.g., Zonyl® FSO and Zonyl® FSN surfactants),manufactured by E.I. DuPont de Nemours and Company; Alkoxylatedsurfactant such as Tego® Wet 510 manufactured from Evonik; fluorinatedPolyFox® nonionic surfactants (e.g., PF159 nonionic surfactants),manufactured by Omnova; or combinations thereof. Suitable cationicsurfactants that may be used in the pre-treatment composition includelong chain amines and/or their salts, acrylated diamines, polyaminesand/or their salts, quaternary ammonium salts, polyoxyethylenatedlong-chain amines, quaternized polyoxyethylenated long-chain amines,and/or combinations thereof.

One surfactant that can be used is an acetylenic diol non-ionicsurfactant, typically present at from 0.05 wt % to 2 wt % based on theink as a whole. An example of an acetylenic diol non-ionic surfactant isSurfynol® 104 (2,4,7,9-tetramethyl-5-decyne-4,7-diol). Other surfactantsthat can be selected for use include polysorbates, C₁₂-C₁₈polyoxyethylene glycol ethers, or a perfluoropolyethers.

Polysorbate surfactants, generally, include Polysorbate 20 (orpolyoxyethylene 20 sorbitan monolaurate), Polysorbate 40 (orpolyoxyethylene 20 sorbitan monopalmitate), Polysorbate 60 (orpolyoxyethylene 20 sorbitan monostearate), Polysorbate 80 (orpolyoxyethylene 20 sorbitan monooleate), or the like. However, not allof these polysorbates have at least 50 wt % lipophilic oleic acid groupsand having an HLB value of less than 15. Brand names for thesepolysorbate surfactants include those sold under the tradename Tween® orAlkest®. Regarding the nomenclature of these polysorbates, the number“20” following “polyoxyethylene” refers to the total number ofoxyethylene —(CH₂CH₂O)— groups found in the molecule. The number 20, 40,60, or 80 following “polysorbate” is related to the type of fatty acidassociated with the polyoxyethylene sorbitan portion. Monolaurate isindicated by 20, monopalmitate is indicated by 40, monostearate by 60and monooleate by 80.

Other polysorbates can likewise be used, including Polysorbate 85, orTween® 85, which is polyethylene glycol sorbitan trioleate; orPolysorbate 81, or Tween® 81, which is a polyoxyethylene (5) sorbitanmonooleate. Tween® 85 and Tween® 81 are oleyl type compounds and include70 wt % oleic acid. Polyoxyethylene sorbitan dioleate can also be used.

Another surfactant that can be used includes polyoxyethylene glycolethers, including those having the base structure, as follows:CH₃(CH₂)_(n)(CH₂CH₂O)_(m)H, where m can be from 2 to 100, but istypically from about 2 to about 20; and n can be from about 8 to 20. Inone particular example, the polyoxyethylene glycol ether can have atolerance of up to 1 “cis” unsaturated (oleyl) group, e.g., 0 or 1 “cis”group (which would reduce the total number of hydrogen atoms by 2 in thebase structure described above, as a double bond would exist along thealkyl chain portion of the formula. Thus, oleyl type surfactants areincluded in this definition, even though they do not strictly fit withinthe above structural formulation, as the formulation is provided merelyfor convenience. Examples surfactants that can be used include Brij® S,Brij® O, Brij® C, and Brij® L type surfactants Synperonic surfactantscan also be used. Specific examples include Brij® S10, Brij® S5, Brij®,S15, Brij® S20, Brij® S2/93, Brij® S7, Brij® 98/O20, Brij® O10, Brij®O2, Brij®, O3, Brij® O5, Brij® C2, Brij® C7, Brij® C10, Brij®, C20,Brij® L4/30, Brij® L9, Brij® L15, Synperonic® 91-2.5, Synperonic®91-2.5, or Synperonic® 91-10, to name a few.

In yet another alternative example, perfluoropolyethers can be included.Some examples can include a primary alcohol or diol, such as Fluorolink®D (HOCH₂CF₂O(CF₂CF₂O)_(p)(CF₂O)_(q)CF₂CH₂OH); Fluorolink® E(HO(CH₂CH₂O)_(n)CH₂CF₂O(CF₂CF₂O)_(p)(CF₂O)_(q)CF₂CH₂(OCH₂CH₂)_(n)OH);Fluorolink® C10 (HOOCCF₂O(CF₂CF₂O)_(p)(CF₂O)_(q)CF₂COOH); or Fluorolink®T (HOCH₂CH(OH)CH₂OCH₂CF₂O(CF₂CF₂O)_(p)(CF₂O)_(q)CF₂CH₂OCH₂CH(OH) CH₂OH),for example. In these examples, p+q can be 20 to 200, or from 40 to 180.Also, p/q can be 0.25 to 5, or can be from 0.5 to 2. n can be from 1 to6, or from 1 to 4, or from 1 to 2.

In the inkjet inks described herein, suitable co-solvents for useinclude water and water soluble organic co-solvents. Any of a number ofsolvents can be used, but in accordance with examples of the presentdisclosure, certain organic co-solvents are used to provide some of thebenefits described herein. Triethylene glycol is one such solvent.Triethylene glycol provides the benefit of acting as a humectantsproviding improved short term decap performance. Additionally, thepresence of a cyclic amide can provide certain benefits, including shortterm and sustained decap, and these solvents can work well with thesurfactants described herein. In one example, there can be two cyclicamides present. For example, a combination of 2-pyrrolidinone andDantocol [di(2-hydroxyethyl)-5,5-dimethylhydantoin] can be particularlyeffective together. Benefits provided by this combination of cyclicamides include assistance with nozzle health and trajectory at certainconcentrations and ratios. It is noted that in one example, the presenceof triethylene glycol, Dantocol, and 2-pyrrolidinone strongly interactwith one another, so formulations that utilize all three tend to performbetter with respect to short term decap, sustained decap, and trajectorythan systems without all three solvents.

Examples of water soluble organic co-solvents that may additionally beused include, but are not limited to, aliphatic alcohols, aromaticalcohols, diols, triols, glycol ethers, poly(glycol) ethers, lactams,formamides, acetamides, long chain alcohols, ethylene glycol, propyleneglycol, diethylene glycols, triethylene glycols, glycerine, dipropyleneglycols, glycol butyl ethers, polyethylene glycols, polypropyleneglycols, amides, ethers, carboxylic acids, esters, organosulfides,organosulfoxides, sulfones, alcohol derivatives, carbitol, butylcarbitol, cellosolve, ether derivatives, amino alcohols, and ketones.For example, co-solvents can include primary aliphatic alcohols of 30carbons or less, primary aromatic alcohols of 30 carbons or less,secondary aliphatic alcohols of 30 carbons or less, secondary aromaticalcohols of 30 carbons or less, 1,2-diols of 30 carbons or less,1,3-diols of 30 carbons or less, 1,5-diols of 30 carbons or less,ethylene glycol alkyl ethers, propylene glycol alkyl ethers,poly(ethylene glycol) alkyl ethers, higher homologs of poly(ethyleneglycol) alkyl ethers, poly(propylene glycol) alkyl ethers, higherhomologs of poly(propylene glycol) alkyl ethers, lactams, substitutedformamides, unsubstituted formamides, substituted acetamides, andunsubstituted acetamides. Specific examples of certain co-solvents thatmay likewise be used include, but are not limited to, 1,5-pentanediol,Liponic ethoxylated glycerol 1 (EG-1), Liponic ethoxylated glycerol 7(EG-7), 2-methyl-2,4-pentanediol, 2-methyl-1,3-propanediol,2-ethyl-2-hydroxymethyl-1,3-propanediol, diethylene glycol,3-methoxybutanol, propylene glycol monobutyl ether,1,3-dimethyl-2-imidazolidinone, and derivatives thereof. Co-solvents canbe added to reduce the rate of evaporation of water in the inkjet ink tominimize clogging or provide other improved properties related toviscosity, pH, surface tension, optical density, gamut, durability,decap, and print quality, for example. The water soluble organicco-solvent system total concentration can range from about 5 wt % toabout 50 wt %, or from 10 wt % to 40 wt %. Each organic co-solvent alonecan be typically present at from about 0.1 wt % to about 20 wt % of theinkjet ink composition. This being said, the solvents may be present inthe inkjet ink composition at any concentration that is effective foruse.

In another aspect of the present disclosure, various biocides can beused to inhibit growth of undesirable microorganisms. Severalnon-limiting examples of suitable biocides include benzoate salts,sorbate salts, and commercial products such as Nuosept®, Ucarcide®,Vancide®, Proxel® GXL, Anticide® B20 or M20, Kordex® MLX, for example.Typically, such biocides include less than about 5 wt % of the inkjetink composition and often from about 0.05 wt % to about 2 wt %.

Additionally, in order to improve durability further, a binder can beincluded in the inkjet inks of the present disclosure as well. Thoughthe addition of a binder can improve durability, too much binder cansignificantly impact decap performance negatively. Thus, a balancebetween decap performance and durability can be considered when addingbinder to the formulations of the present disclosure.

An exemplary binder that can be included in the inkjet ink is a Hydran™RW-7500 or Hydran™ RW-7581 from DIC, which are polyurethane bindersobtained by reacting a polyol containing a vinyl polymer having twohydroxyl groups at one end and at least one polyol. Other suitablebinders that can be used include other water-dispersible or watersoluble polymers. Examples of polymer classes include acrylics,styrenics, polyethylenes, polypropylenes, polyesters, polyamides,(other) polyurethanes, polyureas, polyethers, polycarbonates, polyacidanhydrides, and copolymers and/or combinations thereof. Such polymerparticles can be iono-meric, film-forming, non-film-forming, fusible, orheavily crosslinked, and can have a wide range of molecular weights andglass transition temperatures.

Examples of useful polymeric binders include styrene-acrylic copolymerssold under the trade names Joncryl® (S.C. Johnson Co.), Ucar™ (DowChemical Co.), Jonrez® (MeadWestvaco Corp.), and Vancryl® (Air Productsand Chemicals, Inc.); sulfonated polyesters sold under the trade nameEastman AQ® (Eastman Chemical Co.); polyethylene or polypropylene resinemulsions and polyurethanes (such as the Witcobonds® from Witco);polyacrylic type polymers such as polyacrylic acid and styrene-acrylicmethacrylic acid copolymers (such as Joncryl® 70 from S.C. Johnson Co.,TruDot™ IJ-4655 from MeadWestvaco Corp., and Vancryl® 68S from AirProducts and Chemicals, Inc. These polymers can be used because they arecompatible in typical aqueous-based inkjet ink compositions, and becausethey render printed images that are highly durable towards physicalabrasion. Binders are normally included in the inkjet inks of thepresent disclosure at from 0.1 wt % to 3 wt %, but more typically from0.5 wt % to 2 wt %, based on the polymer solids content.

Other known additives can also be included, as known in the art.

It is noted that, as used in this disclosure, the singular forms “a,”“an,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “an inkjet ink”includes one or more of such inks, and reference to “the pigment”includes reference to one or more amounts of pigments.

As used herein, “liquid vehicle” or “ink vehicle” refers to the liquidfluid in which colorant is dispersed or dissolved to form an ink. Liquidvehicles are well known in the art, and a wide variety of ink vehiclesmay be used in accordance with embodiments of the present disclosure.Such liquid vehicles may include a mixture of a variety of differentagents, including without limitation, surfactants, organic co-solvents,buffers, biocides, viscosity modifiers, sequestering agents, stabilizingagents, and/or water. The liquid vehicle can also carry other additivessuch as latex particulates, binders, or other polymers, in someembodiments. It is noted that though the liquid vehicles of the presentdisclosure can include many of these ingredients, the present technologyrelates more specifically to the use of certain specific organicco-solvents and/or surfactants as set forth herein.

As used herein, “ink” or “inkjet ink” refers to a single liquid vehiclethat contains at least one pigment, and in accordance with embodimentsof the present disclosure, the inks can also include certain morespecific classes of solvents and/or surfactants. In one example, theinkjet ink can be a thermal inkjet ink.

As used herein, “pigment” refers to a colorant particle which istypically substantially insoluble in the liquid vehicle in which it isused. Pigments can be conventionally dispersed using a separatedispersing agent, or can be self-dispersed, having a dispersing agentattached to the surface of the pigment.

As used herein, “self-dispersed” generally refers to pigments that havebeen functionalized with a dispersing agent, such as by chemicalattachment of the dispersing agent to the surface of the pigment. Thedispersing agent can be a small molecule or a polymer or an oligomer.The dispersing agent can be attached to such pigments to terminate anouter surface of the pigment with a charge, thereby creating a repulsivenature that reduces agglomeration of pigment particles within the liquidvehicle.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be “alittle above” or “a little below” the endpoint. The degree offlexibility of this term can be dictated by the particular variable andwould be within the knowledge of those skilled in the art to determinebased on experience and the associated description herein.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not only the numerical valuesexplicitly recited as the limits of the range, but also to include allthe individual numerical values or sub-ranges encompassed within thatrange as if each numerical value and sub-range is explicitly recited. Asan illustration, a numerical range of “about 1 wt % to about 5 wt %”should be interpreted to include not only the explicitly recited valuesof about 1 wt % to about 5 wt %, but also include individual values andsub-ranges within the indicated range. Thus, included in this numericalrange are individual values such as 2, 3.5, and 4 and sub-ranges such asfrom 1-3, from 2-4, and from 3-5, etc. This same principle applies toranges reciting only one numerical value. Furthermore, such aninterpretation should apply regardless of the breadth of the range orthe characteristics being described.

EXAMPLES

The following examples illustrate the embodiments of the disclosure thatare presently best known. However, it is to be understood that thefollowing are only exemplary or illustrative of the application of theprinciples of the present technology. Numerous modifications andalternative compositions and methods may be devised by those skilled inthe art without departing from the spirit and scope of the presentdisclosure. The appended claims are intended to cover such modificationsand arrangements.

Example 1—Magenta Ink Formulations

Various magenta ink formulations were prepared in accordance with Tables1 with difference concentrations of pigment, as follows:

TABLE 1 Ingredient Class Magenta Ink (wt %) 2-Pyrrolidinone OrganicCo-solvent 7.5 Triethylene Glycol Organic Co-solvent 10 Dantocol OrganicCo-solvent 4 Surfynol ® 104 Surfactant 0.3 Brij ® O10 Surfactant 0.3Acticide ® B20 Biocide 0.16 Acticide ® M20 Biocide 0.07 Hydran ™ RW-7581Polyurethane Binder 1.0 PR282 (quinacridone Magenta Pigment Variedpigment) PR150 (azo pigment) Magenta Pigment Varied Water SolventBalance

Example 2—CIE La*b* Color Space

The color saturation data as it relates to FIG. 1 and FIG. 2 wasobtained by measuring CIE La*b* color coordinates and interpolating dataas described herein. It is initially noted that measurements wereobtained using PR282 as the quinacridone pigment, but the data providedin FIGS. 1 and 2 is for a slightly different pigment dispersion, namelya solid solution of PV19 and PR122 (which is very similar to PR282).Essentially, it was determined experimentally that the color propertiesof PR282 compared to the solid solution of PV19 and PR122 as it relatesto red saturation and blue saturation curves were only offset only by0.03 and 0.01 increases in saturation units. These corrections were usedto produce the graphs shown in FIGS. 1 and 2. Graphs related moredirectly to PR282, however, would look very similar to those shown inFIGS. 1 and 2. Thus, for simplicity, the pigment dispersions will bereferred to in this example as the “quinacridone pigment” (referring toPR282 interpolated to PV19/PR122) and the “azo pigment” (referring toPR150).

With specific reference to FIG. 1, color saturation data was obtainedand interpolated using inks with pigment dispersions of blendedquinacridone pigment and azo pigment in accordance with Example 1. Thesemagenta inks were blended at various ratios with a yellow ink, togenerate 13 color patches at constant total ink density. The yellow inkused had the same formulation as the magenta ink but with the followingchanges: the RW-7581 binder was at 0.5 wt %; no Surfynol® 104 was used;and the yellow pigment used was Pigment Yellow 74 at 3.3 wt %. In thisexample, the blended scale ranged from 100 wt % yellow ink to 100 wt %magenta ink. This produced a yellow to red to magenta color ramp, andthus, was repeated using the magenta inks at different weight ratios ofthe quinacridone pigment and azo pigment. The total amount of pigmentsolids used was held constant at 4.2 wt %, and the weight percentagesfor each of four magenta ink (M1-M4) was as follows: M1=4.2 wt %quinacridone pigment; M2=2.9 wt % quinacridone pigment and 1.3 wt % azopigment; M3=2.1 wt % quinacridone pigment and 2.1 wt % azo pigment; andM4=4.2 wt % azo pigment.

For each color patch (13 for each specific magenta ink), the CIE L*a*b*color coordinates were measured using a Gretag-MacBeth Spectrolinaspectrometer equipped with an X-Y table. The red color saturation at ahue angle of 17° was determined by interpolation from the two colorpatches that bracketed a desired hue angle.

The complete CIE La*b* color palette in FIG. 1 was determined using thesame plot as above, but data from additional ramps of yellow to green tocyan and cyan to blue to magenta were also included. For example, theblue and purple color saturations were determined at hue angles of 270°and 315°. In addition, pure color (CMY) ramps and pure color plus addedblack (to go from pure CMY to black) were also included. FIG. 1 was thengenerated by plotting the a*b* data pairs for each color patch. In thiscase, the cyan and yellow inks were the same but the magenta ink wasproduced using 100 wt % quinacridone pigment or 100 wt % azo pigment ata 70:30 ratio.

This color saturation data was used as the input data for astatistically designed experiment using JMP9 Software (SAS Corporation)to produce a predictive model of red, blue, and purple saturation asfunction of the ratio of quinacridone pigment to azo pigment.

With more specific reference to the data present in FIG. 2, variousweight ratios of quinacridone pigment to an azo pigment were plottedagainst the red, blue, and violet color saturation values. These valuesare derived from the statistical model and not from actual experimentaldata. The model allows for interpolation to any combination of thequinacridone and azo pigments, within the range explored (4.2 wt % to 0wt % of each pigment, with total held constant at 4.2 wt %). As can beseen in the graph of FIG. 2, region A indicates an area where anacceptable color balance is struck between blues and reds, whichcorresponds to a weight ratio of 50:50 to 80:20 of quinacridone pigmentto azo pigment. Also shown at region B, an alternative ratio range isshown that also strikes a balance between the pigment dispersions, whichcorresponds to a weight ratio range of about 65:35 to 75:25.

Example 3—Saturation

An ink formulation similar to that described in Example 1 was prepared,except that instead of PR282, a solid solution of PV19 and PR 122 wasused as the quinacridone pigment (at 4.2 wt % total pigment solids). Inthis example, the quinacridone pigment to azo pigment (PR150) weightratio was about 70:30. This ink was printed on eight different types ofmedia, and compared against two commercially available inkjet inks(OfficeJet Pro 8000 and OfficeJet Pro X). A saturation difference wasdetermined by measuring the saturation of Red, Green, and Blue for eachof the commercial inks, and comparing these commercial inks to theinkjet ink prepared in accordance with the present example. Differencein red (ΔRed), difference in green (ΔGreen), and difference in blue(ΔBlue) values were determined. Positive values indicated improvedsaturation for the ink of the present example, and negative numbersindicated lower saturation for the ink of the present example. The datais shown in FIG. 3.

As can be seen, for 5 types of media, there was a significantimprovement in saturation for the magenta ink of the present exampleover the OfficeJet Pro 8000 ink, and almost no change for the remaining3 types of media. However, a general improvement in saturation acrossall colors and all papers was shown for the magenta ink of the presentexample over the OfficeJet Pro X ink.

Example 4—Pigment Settling

A quinacridone pigment (PR282) and an azo pigment (PR150) wereco-dispersed at about a 70:30 weight ratio using a similar dispersantfor each pigment, and the pigment blend was formulated into an inkjetink similar to that described in Example 1. The dispersant used for thepigments was a styrene based resin including at least 60 wt % styrenemonomer units, as well as unsaturated aliphatic carboxylic acid monomerunits having radical polymerizable double bonds, an acid value of 50 to300, and a weight average molecular weight of 7500 Mw to 40000 Mw. Theink was stored in an HP 76 ink supply which is designed to hold 775grams of ink. The 25 cm tall ink supply was stored vertically for 270days without being disturbed. Samples of the ink were then taken fromthe top, middle, and bottom of the container, confirming that while themagenta pigments collectively did settle (UV-vis spectra of bottomsample had more absorbance than the top), the ratio of the two pigmentsdid not change, i.e. the pigments settled together at about the samerate. This was judged by the constant ratio of the 534 nm and 567 nmpeaks throughout (top, middle and bottom) the ink supply column, i.e.the 534 peak being more representative of the PR282 pigment and the 567nm peak being representative of the PR150 pigment. It is noted that bothpigments do overlap in absorbencies, but the relative heights of thepeaks are different for the quinacridone pigment and the azo pigment.

While the present technology has been described with reference tocertain examples, those skilled in the art will appreciate that variousmodifications, changes, omissions, and substitutions can be made withoutdeparting from the spirit of the disclosure. It is therefore intendedthat the disclosure be limited only by the scope of the appended claims.

What is claimed is:
 1. A magenta ink, comprising: a liquid vehicleincluding water, organic co-solvent, and surfactant; and from 2 wt % to9 wt % of a magenta pigment blend suspended therein, said magentapigment blend comprising: quinacridone pigment having the generalformula:

wherein R₁ and R₂ are each independently H, a halogen atom, or a C₁ toC₄ alkyl group, and azo pigment having the general formula:

wherein R_(a) is H, aryl, or C₁ to C₄ alkyl, wherein when R_(a) is aryl,the aryl is not a phenyl group having at least one hydrogen that hasbeen substituted with a chlorine atom; wherein R_(b) and R_(d) areindependently H, a C₁ to C₄ alkyl, an oxygen-containing functionalgroup, a nitrogen-containing functional group, or a sulphur-containingfunctional group; wherein R_(c) is H; and wherein the weight ratio ofquinacridone pigment to the azo pigment is from 50:50 to 80:20 bypigment solids content.
 2. The magenta ink of claim 1, wherein thequinacridone pigment comprises a solid solution of Pigment Violet 19 andPigment Red 122, or the quinacridone pigment comprises Pigment Red 282.3. The magenta ink of claim 1, wherein the azo pigment comprise PigmentRed
 150. 4. The magenta ink of claim 1, formulated as an inkjet ink. 5.The magenta ink of claim 1, wherein the surfactant comprises anacetylenic diol non-ionic surfactant, a polysorbate surfactant, orC₁₂-C₁₈ polyoxyethylene glycol ether surfactant, a perfluoropolyethersurfactant, or a combination thereof.
 6. The magenta ink of claim 1,wherein the organic co-solvent comprises triethylene glycol, a cyclicamide, or a combination thereof.
 7. The magenta ink of claim 6, whereinthe cyclic amide comprises 2-pyrrolidinone,di-(2-hydroxyethyl)-5,5-dimethylhydantoin, or mixture thereof.
 8. Themagenta ink of claim 1, wherein the ink is devoid of dye.
 9. The magentaink of claim 1, further comprising from 0.1 wt % to 3 wt % polymericbinder.
 10. The magenta ink of claim 1, wherein the quinacridone pigmentand the azo pigment are both dispersed in a manner such that settlingwithin the magenta ink over a period of 270 days is such that a weightratio of quinacridone pigment to azo pigment anywhere within the ink iswithin ±3% compared to initial ratio measurements.
 11. The magenta inkof claim 1, wherein the weight ratio of quinacridone pigment to the azopigment is from 70:30 by pigment solids content.
 12. The magenta ink ofclaim 1, wherein the quinacridone pigment consists of PR 282 and the azopigment consists of PR
 150. 13. The magenta ink of claim 1, wherein themagenta pigment blend is present in the ink composition from 2 wt % to4.2 wt %.